Recirculating (ductless) exhaust fans are not allowed if mechanical ventilation of a space is required, but such fans are allowed in naturally ventilated spaces.
They are completely California Title 24 and Energy Star compliant.
A ductless bathroom fan can perform the same job as a ducted bathroom fan but requires less space. Ductless bathroom fans come in a variety of style options and can be installed in any bathroom.
Bathroom fan installation requires outside ventilation. If the bathroom exhaust fan or venting fan isn't accessible through an attic, you'll need to vent through a sidewall of your house.
Benefits of Using Ductless Bathroom Fans
Mold reduction: Since you have a constant flow of air, it prevents mold from growing. When paired with a window, you can reduce moisture growth in the bathroom, providing the one-two punch that'll keep mold growth at bay.
“If a bathroom is not properly vented many possible issues could arise,” says indoor air quality expert Dave Jones. These issues include mold, rot or paint damage. In my first home, the bathroom fan vented into the attic instead of outside, causing major mold damage.
The correct installation and proper maintenance of bathroom fan ducts is essential to ensure that the fan functions properly and no damage is caused to your home, apartment, or commercial building.
This section states that vented air needs to be sent to the exterior and not into an interior space such as an attic. The fan minimum is 50 cubic feet per minute (cfm) intermittent or 20 cfm continuous.
The installation of a recirculating exhaust fan is one of the easiest ways to vent a bathroom without an exterior exit. Recirculating fans filter the air via a set of charcoal or HEPA filters before releasing it back into the bathroom, in contrast to ordinary exhaust fans, which exhaust air outside.
New NEC® Section 422.18(B) states that metal parts of ceiling-suspended (paddle) fans in bathrooms and shower spaces shall not be located within a zone measured 3 feet horizontally and 8 feet vertically from the top of the bathtub rim or shower stall threshold.
Recirculating fans, used when venting outside isn't an option, do offer some odour control by trapping dust and particles in a filter. However, they don't address moisture effectively. The trapped moisture needs regular filter changes to maintain functionality.
Use Exhaust Fans Wisely
As you might expect, exhaust fans can have a negative impact on attempts to heat your home, allowing warm air to escape and giving the cold Michigan air an entry point to the interior.
Venting your bathroom fan into the attic is not allowed by building codes in many areas. If you also plan to sell your home, you can run into problems if your home is not up to code.
For bathrooms 50 square feet and smaller, it's recommended you purchase a bath fan designed for small rooms. In other words, choose under 79 CFM bath fans. For medium-sized bathrooms, use 80 to 99 CFM bath fans. For large bathrooms that are over 100 square feet but under 150 square feet, use over 100 CFM bath fans.
Although not Code required, bathroom GFCI(s) should be on separate circuits. This eliminates tripping from high draw hair dryers and spa equipment. Ceiling exhaust fans, overhead lighting and cabinet lighting can be on with other lighting up to a maximum of 12 fixtures.
Ductless bathroom vent fans can be legit, especially if you have a window for natural ventilation. While they might not be as powerful as vented options, they're still effective in reducing humidity and preventing mold.
The moist air will fuel the growth of mold and mildew on the roof framing and the sheathing that covers the timbers. Wood rot is an absolute certainty over time if you dump bath exhaust into an attic. This moist air must exhaust to the exterior of your home. This is non-negotiable.
Without an exhaust fan, you can expect to have mold growing in your shower, peeling paint, and even damaged drywall. Prolonged moisture buildup is a disaster for the bathroom; picture damaged walls, floors, ceilings, fixtures, and even doors. That's something no homeowner wants to face!
For purposes of this specific discussion, let's center things around the way a bathroom fan is vented. Now, if you were to ask where “should” bathroom fans be vented to, the answer is to the outside of the house. (and, yes, if installing a roof vent, it should obviously be properly flashed).
Method One: Calculating Standard Bathroom Exhaust Fan Size
The most common way to size a bathroom fan is using the calculation of 1CFM per square foot of floor area. To work out the floor area, simply take a tape measure and multiply the length and width of the bathroom (including shower and bath areas).
For better performance, duct runs should be as straight as possible. If a bend is necessary, 2 to 3 feet of straight duct should be allowed to run from the fan exhaust port to the first elbow in the duct run.
Yes, Flex ducts are a perfectly valid option to use a conduit for your bathroom exhaust fan.
Use of a Ceiling Vent
Installing a ceiling vent is probably the most efficient way to ventilate a bathroom with no outside access. A ceiling vent is a unique machine that allows air to escape from the bathroom.
Building regulations dictate that in most cases, exhaust fans must be ducted to the outside, and not into a ceiling or wall cavity. For optimal performance of your exhaust fan, it's important to keep duct runs as short as possible and without excessive bends.